Many infectious diseases require relatively close contact for the disease to be transmitted. For example, Severe Acute Respiratory Syndrome (“SARS”) is spread through droplets of phlegm from a sneeze or cough. This requires two persons to be reasonably close—within a few meters of each other—for disease transmission.
When a patient is suspected of having a contagious disease requiring close contact for transmission, all those with whom the patient has come into close contact since contracting the disease need to be found to determine if they have also contracted the disease. This is presently conducted by circulating notices, and asking the patient. As the patient may by that stage be quite ill, this ability to recall all close contacts over several days is quite limited. If the patient is elderly, or a child, it will be severally limited. Unintentional close contact can also occur in places such as, for example, a lift where the patient will not know the identity of the persons with whom the lift was shared, or when a person uses a lift that was used by an infected patient within a transmission time of the disease.